Check Valve Question

Discussion in 'Bubba's Outboards' started by BKS72, Mar 25, 2008.

  1. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    I put a new 23 gal. below deck tank in my boat this winter (motor is a 1980 75hp OMC). I put it up front, so it's about 20' from the motor. It primes fine with the bulbs (I put 2 in, one up front, one in back near the motor). The fitting on top of the tank is a barbed fitting with a check valve in it that only lets fuel go out, not drain back in. I'm guessing that it's there for inboard applications to keep fuel from draining out of the lines and losing prime, but like I said, that's just a guess.

    I have to baby it to get it up to full throttle or it will starve out and die. It's also tough to start since it seems to need to be at high RPM to draw fuel. Once I coax it up to about half throttle, she runs well and throttle response is good. My questions are:

    1. Could that check valve require more vacuum than my fuel pump can put out at low RPM to open, so takes a while before it will build enough vacuum to open it up to let enough fuel reach the carbs?

    2. Will it hurt anything to take it out? I can't see where it would, but I'm not sure.

    Carburetors were just rebuilt late last summer, fuel pump is new, and the plugs were just replaced before I put it away (with Sta-bil) for the winter. Thanks in advance!!

    Branden
     
  2. slowboat

    slowboat New Member

    Messages:
    196
    State:
    Ohio
    Its called a siphon valve used to keep gas from draining back to tank.
    I had to remove the one in my boat because the pump wasn't strong enough to pull through it when you open it up it would die. After removing it works ok...sb hope this helps
     

  3. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    Actually, it's called an anti-siphon valve. Designed to keep fuel in the tank and not siphon out into the bilge, in case of a fuel line break.

    They are notorious for going bad. Be sure your fuel line has a large enough inside diameter, and no kinks or restrictions.

    You can replace your anti-siphon valve with an open hose barb, and see if you've got the same problem
     
  4. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    Thanks you guys! I was wondering why it was there. I'll swap it out for an open fitting and see what happens.

    Do you guys know typically how much vacuum a fuel pump would pull on a motor like mine (1980 E'rude 75)? I'm just curious. Thanks again,

    Branden
     
  5. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    OK, swapped the check valve out for an open fitting and it's still giving me fits to start. Acts like it's not getting enough fuel when I try to start it and have to baby it up to full throttle. After I run it for awhile she's OK, but then acts like it's loading up (smokes like a pig) when I go to start it again.

    I'll check all my fuel lines at the motor and I have a fresh set of plugs for it and I'll pick up a spark-tester this afternoon. While I'm changing plugs I'll throw the compression tester on it just for giggles since I'll be in it anyway. Anything else I need to check?

    I'll run some sea-foam through it as well, and if it's not any of the above and the sea-foam doesn't help it, I'll assume I need to yank the carbs and clean them up. Thanks in advance for any advice!

    Branden
     
  6. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    How big of a fuel line does it have from the new tank and find you a barbed splicer and take one of the bulbs out of line and see if that helps. You do know that there is a check valve inside those primer bulbs also.
     
  7. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    3/8 line. I'll pull that first bulb up front and check that - Thanks Bubba! I think the one at the back will have enough pull to get the fuel where I need it.

    It ran fine last fall so the only thing that's changed is the fuel tank location and the addition of the extra bulb and water separator from
    Wal-Mart that I've heard mentioned on here a couple of times.

    Will that water filter work for particulate matter as well or do I need an additional filter to take out dirt? Thanks again!

    Branden
     
  8. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    That one filter will do the job.
     
  9. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    Everything checked good (spark, compression, etc), so I yanked that 2nd fuel bulb and that did the trick. She ran great today. Thanks for all the help!!

    Branden
     
  10. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    glad you found it and thanks for the follow up it helps to know when something helps.